This invention is for aluminum phosphate compositions which are characterized by having both high porosity and phosphorus-to-aluminum (hereinafter "P/Al") ratios near unity. The high porosity of these compositions is characterized by a combination of high pore volume and low surface area, resulting in high average pore diameter. These compositions are useful as cracking catalysts, supports for ethylene polymerization catalysts, flatting agents, carriers, adsorbents and thickeners.
Synthetic aluminum phosphates are known and the utility and properties of various compositions have been discussed extensively in the literature. For example, Kearby, 2nd Int'l Congress and Catalysis, "New AlPO.sub.4 Gels As Acid Catalysts," pp. 2567-2579 (1960, Paris) and Moffat, Catal. Rev. - Sci. Eng., "Phosphates As Catalysts," Vol. 19, pp. 199-258 (1978) discuss the properties of various aluminum phosphates, reporting surface areas of about 200.0 to 500.0 m.sup.2 /gm and pore volumes (hereinafter "PV") of about 0.45 to 0.78 cc/gm.
Aluminum phosphate-containing compositions also have been described, as in U.S. Pat. No. 3,904,550 (Pine) which discloses a catalyst support comprised of alumina and aluminum phosphate with P/Al=0.54 and PV=1.34 cc/gm; U.S. Pat. No. 4,210,560 (Kehl) which discloses magnesia-alumina-AlPO.sub.4 catalyst supports with P/Al=0.21 and PV=1.11 cc/gm or with P/Al=0.69 and PV=0.72 cc/gm; and Marcelin et al., J. of Catal., "Alumina-Aluminum Phosphate As Large-Pore Support and Its Application to Liquid Phase Hydrogenation," Vol. 83, pp. 42-49 (1983) which discloses alumina-aluminum phosphate supports with P/Al=1.0 and PV=0.32 cc/gm or with P/Al=0.5 and PV=0.64 cc/gm.
U.S. Pat. Nos. 4,364,842 and 4,444,965 (McDaniel et al.) disclose aluminum phosphate-containing catalyst bases in which P/Al=0.7-0.9 and in which the highest PV disclosed was 0.84 cc/gm (for P/Al=0.80).
Many of the prior art compositions share the same limitation. As the P/Al approaches unity, the pore volume of the prior art compositions decreases. Typically, aluminum phosphate compositions were not prepared with both these characteristics: a P/Al near unity and a high pore volume (i.e., PV of at least 1.0 cc/gm). High pore volume is very desirable for aluminum phosphate compositions used as polymerization catalysts due to their polymerization characteristics.
U.S. Pat. No. 3,342,750 (Kearby) discloses aluminum phosphate gels with PV of 1.39-1.56 cc/gm and surface area (hereinafter "SA") of 427-523 m.sup.2 /gm, resulting in average pore diameters of 65-114 Angstroms. Kearby teaches a high PV composition which also has a P/Al near unity, but it can be seen that the high PV is achieved at the expense of pore diameter, which is low. It is taught, in U.S. Pat. No. 4,769,429 (Furtek), that high average pore diameter is a very desirable characteristic for polymerization catalysts. In providing catalysts supports with high PV and low SA, the compositions of the invention achieve this combination of properties and provide aluminum phosphate catalyst supports having high average pore diameters.